Computers and other systems have used disk drives for many years to store large amounts of digital information. This is because while computers and other systems may have sufficient main memory (such as random access memory) to perform ongoing computational tasks, when storing large amounts of data, such as an operating system, application programs, or program data, a mass storage device such as a disk drive is usually required.
While there are many types of disk drives, including floppy disks and optical disks, probably the most widely used is the hard disk drive. A hard disk drive can record massive amounts of digital information on concentric memory tracks of a magnetic medium that coats one or more disks. The digital information is recorded as magnetic transitions within the magnetic medium. The disks are mounted on a spindle and turned at very high speeds by a spindle motor. Information on the disks is accessed using magnetic read/write heads located on pivoting arms that move over the disks. The read/write heads must be accurately aligned with the memory tracks to ensure proper reading and writing of digital information.
Hard disk drives require more than just mechanical components. Modern hard disk drives include sophisticated disk electronics that include an interface for receiving and transmitted signals and data from and to external devices, and a Head Disk Assembly Interface for interfacing the disk electronics to a head disk assembly. The head disk assembly includes the disks, the read/write head(s), the spindle motor that rotates the disks, a servo-operated actuator arm that moves the read/write head(s), and other disk drive components. The disk electronics also include servo drivers to move the actuator arms, motor drivers to drive the spindle motor, write drivers to drive the read/write head(s) to write data, an amplifier to amplify data being read, logic to determine where particular data is to be written to or read from, and data formatting electronics to convert incoming data to the proper format for writing and for converting outgoing data to the proper format for the external system. Generally, the disk electronics are operated under the control of a processor.
To enable higher speeds and improved performance, modern disk electronics include disk buffer memory (RAM) for temporarily storing data. For example, disk buffer memory can store data that has been read until data integrity checks have been performed to ensure that the read data is not corrupted, or until an external device calls for that data. Disk buffer memory can also be used to store both prefetched data and data that is to be written to the disk. Disk buffer memory has proven so useful that disk drive users are demanding additional memory.
While hard disk drives have proven themselves to be very useful recording devices, hard disk drive manufacturing is a highly competitive business subject to small profit margins. Adding additional disk buffer memory to the disk electronics could reduce or even eliminate that profit margin. Therefore, there is a need in the art to provide additional disk buffer memory with little or no increase in costs. While the foregoing has described a hard disk drive, the issues of costs and the benefits of disk buffer memory exist in other types of mass memory devices, specifically including optical drives. Therefore, a general method of using main memory as disk buffer memory would be useful.